1. Field of the Invention
The present invention relates to an automatic diaphragm control camera of the T.T.L. (through the lens) light measurement type in which scene light is measured through an objective and a diaphragm aperture being stopped-down, and in which the stopping down operation is stopped by means of an electromagnetic means when the diaphragm reaches an aperture size proper for the intensity of the scene light and set exposure parameters such as a set film sensitivity and a set shutter speed.
2. Description of Prior Art
In cameras of the aforementioned type, it is desired that the diaphragm aperture is left fully opened in the case of daylight photographing with a low brightness condition where an optimum exposure is obtained with the diaphragm set to the fully opened aperture. However, it has been difficult for prior art cameras of the aforementioned type to provide such a fully opened aperture in such cases. This is assumed to be due to the fact that a slight time lag is unavoidable from generation of a diaphragm stop control signal until actual arresting of the diaphragm by a diaphragm arresting electromagnetic means responsive to the diaphragm stop control signal, such that the diaphragm is stopped-down more than is necessary during the aforementioned time lag. Additionally, the mechanical play among, and/or between, the various mechanical linkages from the diaphragm arresting electromagnetic means to a diaphragm stop or arresting member varies with individual cameras. Also, the magnetic force required for pressing the armature of the electromagnetic means to its pole, for example, varies from one to another of individual electromagnetic means incorporated in cameras.
In U.S. Pat. No. 4,339,186 filed on May 1, 1981 and assigned to the same Assignee, there has been proposed automatic diaphgram control cameras of the aforementioned type which eliminate the drawback of prior art cameras. More particularly, the cameras proposed therein are provided with a discrimination means which generates a diaphragm stopping-down prevention signal when it determines that the diaphragm is to be set to a fully opened aperture. A diaphragm release control means deactivates a diaphragm stopping-down release electromagnetic means upon receipt of the diaphragm stopping-down prevention signal. Thus, upon generation of the diaphragm stopping-down prevention signal, no actual diaphragm stopping-down operation occurs and the diaphragm is exactly set to the fully opened aperture. However, a problem occurs with the proposed cameras in the case of flash photography for which the diaphragm is to be stopped-down to a smaller aperture in dependence upon the guide number of a flash device and/or a camera-to-object distance, because the scene is generally dark and the diaphragm is automatically set to a fully opened aperture when flash illumination is necessitated.